Simultaneous denitrification and methanogenesis in an anaerobic expanded bed reactor

Wastewaters from some industries contain high levels of nitrate but an insufficient amount of electron donor to sustain biological denitrification. An option of treatment is combining anaerobic digestion and denitrification process in a single unit. During this research, an anaerobic expanded bed reactor was operated at different C/N ratios (10, 7, 4, 3, 2 and 1) in order to study nitrogen and organic matter removal. A 3 L reactor was used with a flow feed of 3 L/d, upflow velocity of 7 m/h and temperature between 30-35°C. Organic matter removal remained above 90% throughout the 177 days of experimentation. Nitrogen removal was over 90%, when C/N ratios were greater than the stoichiometric (C/N>1), however, with a ratio C/N=1, nitrogen removal was 60%, causing the accumulation of nitrite. The high removal of nitrate and organic matter reached in this study demonstrate the viability to use this type of reactors for the treatment of such efluents, in spite of the fact that the increase of nitrate concentration changed the biomass distribution, which caused a decrease in the size of anaerobic granules.